The present invention relates to field coils of dynamoelectric machine rotors and, more particularly, to the end turn section of a rotor field coil of a superconducting electrical generator.
Generator rotor coils which are not superconducting are subjected to centrifugal forces due to the rapid rotation of the rotor during operation. In typical designs, these forces are compensated for by a retaining ring which is securely fastened around the radially outward surface of the end turn section of the rotor coil. In conventional generators, the rotor winding is not subjected to significant forces in either the axial or circumferential directions.
Rotor coils of a superconducting generator, in contrast to the coils of the conventional nonsuperconducting rotor described above, experience substantial axial and circumferential forces due primarily to the fact that a stator of a typical superconducting generator does not utilize a laminated core to contain its stator coils. The resulting flux paths, therefore, do not pass through the teeth of a stator coil. Instead they are directed in such a way as to exert significant forces on the rotor coil in varied directions.
For these reasons, the end turn section of a superconducting rotor's field winding requires rigid support in the axial and circumferential directions besides the normal radial support requirements due to the centrifugal forces described above. If the coils are not rigidly constrained, the axial and circumferential forces described above will cause the coils to move and experience a temperature rise caused both by frictional effects and the work performed during this motion. Any creation of heat within the rotor coils will have a deleterious effect on the cryostability of a superconducting rotor and must therefore be avoided.
Another significant difference between conventional and superconducting rotor coil support requirements is that a superconducting rotor coil utilizes a conductor which is more flexible and of a smaller cross-sectional area than the larger, more rigid rotor coil of a conventional generator. The smaller, flexible conductor is more difficult to wind because of its tendency to migrate from its desired physical position during the rotor winding operation.
It should therefore be apparent that the smaller, flexible conductor of superconducting rotors, which are subjected to multidirectional forces during operation, require a winding configuration and technique to compensate for these physical conditions which are significantly different than those customary in conventional rotor field coils.
The present invention provides physical support in the radial, circumferential and axial directions to prevent the above-described forces from causing motion in the rotor coils during operation. Furthermore, an end turn winding made in accordance with the present invention is tilted from a directly radial configuration in order to facilitate its construction during the winding operation.
The rotor conductors are associated in a conductor stack that is supported by an arcuate support block that has a generally L-shaped cross-section. The conductor stack is electrically insulated from the support block by a plurality of arcuate insulative members with wedge-shaped cross-sections. A rigid end turn cylinder is placed radially outward from the support block and conductor stack with a rigid retaining tube disposed radially outward from the end turn cylinder.
The above-described configuration provides substantial coil support in all directions while permitting the conductor stack to be wound in a tilted, as opposed to radial, configuration.